Air strut suspension system for a self-propelled high ground clearance product applicator

ABSTRACT

A system, apparatus and method for controlling the height of a frame of a self-propelled high ground clearance, agricultural product applicator above a ground surface utilize a trailing link suspension system including an extensible air strut, for connecting ground engaging wheels of the applicator to the frame of the applicator. The trailing arm suspension system includes an upper suspension arm attached to the frame, a lower suspension arm providing sole support of a ground engaging wheel attached to the lower arm, and the extensible air strut interconnected between the upper and lower arms. Height of the applicator above the ground surface is controlled by regulating a flow of pressurized air to the air strut, to thereby control extension of the air strut.

FIELD OF THE INVENTION

This invention relates generally to a self-propelled agriculturalproduct application implement, such as a high-clearance sprayer and/orspreader, and more particularly to a suspension system for suchimplements.

BACKGROUND OF THE INVENTION

Modern agricultural practices rely heavily on precise and timelyapplications of fertilizers, herbicides, pesticides and other chemicals.In situations where the applications must be made to standing row crops,such as corn or beans, liquid or granular materials are often appliedusing a high ground clearance, self-propelled applicator.

In order to provide maximum ground clearance, such applicators utilizehighly specialized suspension systems for connecting the ground engagingwheels of the applicator to a frame of the applicator. Typically,separate hydraulic drive motors are provided as part of the suspension,for each drive wheel, to thereby further enhance ground clearance byminimizing the encroachment of drive line or typical suspensioncomponents into the space between the wheels under the applicator.

In the past, suspension systems for high ground clearance,self-propelled applicators utilized suspension components, includingcompression springs and hydraulic shock absorbers, that were essentiallythe same as those used in automotive and commercial vehicle suspensions.While these components have generally worked well in the specializedsuspension systems of high ground clearance, self-propelled applicators,they are not ideal and further improvement is desirable.

One problem with prior high clearance applicator suspension systems, isthat the ground clearance tends to vary depending upon how heavily theapplicator is loaded. Initially, as it pulls away from a tender with afull load, an applicator is typically carrying several thousand poundsof a product to be applied. As the product is dispensed onto the fieldby the applicator, the weight of the remaining product being carried bythe applicator gradually decreases to zero. With prior suspensions thatrely on compression springs for supporting the load carried by theapplicator, ground clearance starts out at a minimum when the applicatoris initially fully loaded, with the springs compressed to their lowestworking height. As product is dispensed and load on the applicatordecreases, the compression springs extend from their initiallycompressed state, and raise the applicator higher above the groundsurface.

Having ground clearance vary is undesirable for at least two reasons.First, the effectiveness of the product being applied is highlydependent upon precise application. As ground clearance changes, sprayor granular spreading patterns may be adversely affected, requiringcontinual compensating adjustments to be made by an operator of theapplicator, in order to maintain optimal product application. Second,ride quality and handling characteristics of the applicator aretypically affected by ground clearance, and the state of extension ofthe compression springs. The springs, and hence the suspension, isconsiderably stiffer when the springs are more fully compressed thanwhen they are extended.

Prior suspension systems using compression springs are also typicallyoptimized for one type of operating mode. This results in compromisingsuspension performance in other operating modes that are typicallynecessary in practical utilization of the applicator. For example, it isnecessary to drive the applicator across the field in an unloaded state,to and from the tender, in addition to driving the vehicle across thefield in a fully or partially loaded state while applying product to thefield. It will likely be necessary for the applicator to travel onpublic roads, at times, in moving between fields. Differences inhandling characteristics inherent in spring-based suspension systems,from loaded to unloaded states of the applicator, may make such on-roadtransit more difficult. It may be necessary to transport the applicatoron a truck or trailer between fields. This can present additionalproblems for high ground clearance applicators, in that the overallcombined height of the applicator and the bed of the trailer or vehiclecarrying the applicator may exceed applicable limits for transport onpublic roads.

It is desirable, therefore, to provide an improved suspension system forself-propelled, high ground clearance, agricultural product applicators.It is particularly desirable to provide such an improved suspensionsystem that can set and maintain a desired ground clearance, and providedesirable ride and handling characteristics in a self-propelled, highground clearance, agricultural product applicator throughout a widerange of operating modes and conditions.

SUMMARY OF THE INVENTION

The invention provides a system, apparatus and method for controllingthe height of a frame of a self-propelled agricultural productapplicator above a ground surface, by using a trailing link suspensionsystem including an extensible air strut for connecting ground engagingwheels of the applicator to the frame of the applicator. The trailingarm suspension system includes an upper suspension arm attached to theframe and a lower suspension arm providing sole support of a groundengaging wheel attached to the lower arm. The extensible air strut isinterconnected between the upper and lower arms in such a manner thatthe height of the applicator above the ground surface may be controlledby regulating a flow of pressurized air to the air strut, to therebycontrol extension of the air strut and vertical distance between arolling axis of the wheel and the frame of the applicator.

In one form of the invention, a trailing-arm suspension system isprovided, for operatively connecting a ground engaging wheel to a frameof a self-propelled agricultural product applicator. The frame of theapplicator is adapted for supporting at least one product container. Theframe defines forward and rear ends of the frame, a longitudinallyextending central axis of the frame extending from the rear to the frontof the frame in a direction of travel of the applicator, and a verticalaxis of the frame. The suspension system may include, a lower suspensionarm, an upper suspension arm, and an air strut that are operativelyinterconnected to one another and disposed between the ground engagingwheel and the frame, for supporting the applicator above a groundsurface.

The upper suspension arm defines a frame attachment point of the uppersuspension arm, that is adapted for fixed attachment to the frame. Thelower suspension arm defines a rolling axis of the ground engagingwheel, and is adapted for supportive attachment thereto of the groundengaging wheel for rotation of the ground engaging wheel about therolling axis of the wheel. The upper and lower suspension arms alsodefine respective forward and aft ends of the suspension arms, with theforward ends being joined to one another in a pivoting connection, forpivoting movement of the lower arm with respect to the upper arm about asuspension pivot axis that extends generally parallel to the rollingaxis of the wheel and is located forward of the rolling axis of thewheel. The aft ends of the upper and lower suspension arms are locatedrespectively aft of the frame attachment point and rolling axis, and arerespectively adapted for connection to upper and lower ends of the airstrut.

The air strut may have an upper end thereof adapted for operativeattachment to the aft end of the upper suspension arm, and may also havea lower end, of the air strut, adapted for operative attachment to theaft end of the lower suspension arm. The air strut may be configured forreceiving a flow of pressurized air from an air power source, and forextending and retracting in response to the flow of pressurized air, tothereby respectively lower and raise the rolling axis of the wheel withrespect to the frame attachment point. The air strut includes an aircylinder and piston arrangement with rigid walls that do not flex likeelastomeric air springs. In some forms of the invention, the air strutmay include a shock absorber.

In some forms of the invention, the upper suspension arm may be rigid,and configured to not articulate vertically with respect to the frame,with the forward end of the upper suspension arm being located bothforward of and below the frame attachment point.

In some forms of the invention, the suspension system may provide solesupport for the ground engaging wheel attached to the lower arm of thesuspension system. Some forms of a suspension system, according to theinvention, may further include a hydraulic motor drive unit operativelyattaching the wheel to the lower suspension arm.

Some forms of a trailing-link suspension system, according to theinvention, may further include an electronic control unit that isoperatively connected and configured for controlling the flow ofpressurized air to the air strut from the air power source, to therebycontrol extension and retraction of the air strut. An electronic controlunit, according to the invention, may also be configured to receive aninput signal indicative of a desired height of the frame of theapplicator above a ground surface beneath the applicator, and forcontrolling the air power source in a manner causing the air strut andsuspension to support the frame at the desired height.

The invention may also take the form of a self-propelled agriculturalproduct applicator, having at least one ground engaging wheeloperatively connected to a frame by a trailing-arm suspension system inaccordance the invention. Some forms of a self-propelled agriculturalproduct applicator, according to the invention, may have two or moreground engaging wheels, each operatively attached to the frame byindividual trailing arm suspension systems according to the invention.

A self-propelled agricultural product applicator having two or moreground engaging wheels each operatively attached to the frame byindividual trailing arm suspension systems according to the invention,may also include an electronic control unit operatively connected forcontrolling the flow of pressurized air to the air struts of thesuspension systems of the two, or more, ground engaging wheels from theair power source, to thereby control extension and retraction of the airstruts. In some forms of the invention, an electronic control unit maybe configured to receive an input signal indicative of a desired heightof the frame of the applicator above a ground surface beneath theapplicator, and for controlling the air power source in a manner causingthe air struts of the suspension systems of the two, or more, groundengaging wheels to support the frame of the applicator at the desiredheight.

The invention may also take the form of a method for controlling theheight of a frame of a self-propelled agricultural product applicatorabove a ground surface, by connecting the frame to a ground supportingwheel of the applicator using a trailing link suspension systemincluding an upper suspension arm attached to the frame, a lowersuspension arm providing sole support of a ground engaging wheelattached thereto, and an extensible air strut operatively interconnectedbetween the upper and lower arms, and controlling a flow of pressurizedair to the air strut, to thereby control extension of the air strut andheight of the applicator frame above the ground surface.

A method, according to the invention, may also include connecting two ormore ground engaging wheels of the applicator to the frame usingindividual trailing link suspension systems, each including an uppersuspension arm attached to the frame, a lower suspension arm providingsole support of a ground engaging wheel attached thereto, and anextensible air strut operatively interconnected between the upper andlower arms, and controlling a flow of pressurized air to the air strutsof the suspension systems, to thereby control respective extension ofthe air struts and height of the applicator frame above the groundsurface.

In various forms of a method according to the invention, the uppersuspension arm may define a frame attachment point thereof, adapted forfixed attachment to the frame. The lower suspension arm may define arolling axis of the ground engaging wheel, and be adapted for supportiveattachment thereto of the ground engaging wheel for rotation of theground engaging wheel about the rolling axis of the wheel. The upper andlower suspension arms may also define respective forward and aft endsthereof, with the forward ends being adapted for operative pivotingconnection to one another about a suspension pivot axis extendinggenerally parallel to the rolling axis of the wheel and disposed forwardof the rolling axis of the wheel. The aft ends of the upper and lowersuspension arms may be disposed respectively aft of the frame attachmentpoint and the rolling axis, with the aft ends of the upper and lowersuspension arms being respectively adapted for operative attachmentthereto of the air strut. The air strut may have an upper end thereofadapted for operative attachment to the aft end of the upper suspensionarm, and may also have a lower end thereof adapted for operativeattachment to the aft end of the lower suspension arm. The air strut maybe configured for receiving a flow of pressurized air from an air powersource, and for extending and retracting in response to the flow ofpressurized air, to thereby respectively lower and raise the rollingaxis of the wheel with respect to the frame attachment point.

Other aspects, objects and advantages of the invention will be apparentfrom the following detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thespecification illustrate several aspects of the present invention and,together with the description, serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a perspective illustration of an exemplary embodiment of aself-propelled, high ground clearance, agricultural applicator,according to the invention;

FIG. 2 is a perspective illustration of a frame and suspension systemsof the exemplary embodiment of the applicator of FIG. 1;

FIG. 3 is an exploded perspective illustration of a suspension system ofthe exemplary embodiment of the applicator shown in FIG. 1;

FIG. 4 is an assembled perspective illustration of the suspension systemshown in FIG. 3; and

FIGS. 5-7 are orthographic illustrations of the suspension system ofFIG. 4, showing the suspension system respectively in maximum height,working height, and minimum height positions.

While the invention will be described in connection with certainpreferred embodiments, there is no intent to limit it to thoseembodiments. On the contrary, the intent is to cover all alternatives,modifications and equivalents as included within the spirit and scope ofthe invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 shows an exemplary embodiment of the invention in the form of ahigh ground clearance, self-propelled, agricultural product applicator10, that includes improved suspension systems 12, according to theinvention, for each of the four ground engaging wheels 14 of theapplicator 10.

As shown in FIGS. 1-4, and described in more detail below, the inventionprovides a system, apparatus and method for controlling the height 16 ofa frame 18 of a self-propelled agricultural product applicator 10 abovea ground surface 20, by using a trailing link suspension system 12 thathas an extensible air strut 22, for connecting each of the four groundengaging wheels 14 of the applicator 10 to the frame 18 of theapplicator 10. The trailing arm suspension systems 12 each include anupper suspension arm 24 attached to the frame 18, and a lower suspensionarm 26 that provides sole support of a ground engaging wheel 14 attachedto the lower arm 26, in a manner described in more detail below.

As illustrated in FIGS. 4-7, the extensible air strut 22 isinterconnected between the upper and lower arms 24, 26 in such a mannerthat the height 16 of the applicator 10 above the ground surface 20 maybe controlled by regulating a flow of pressurized air to the air strut22, to thereby control extension of the air strut 22 and a verticaldistance 28 between a rolling axis 30 of the wheel 14 and the frame 18of the applicator 10. As shown in FIGS. 5-7, by controlling the flow ofpressurized air to the strut 22, the suspension can be positioned andheld at desired working height position 32, as shown in FIG. 6, or anyother height position between a highest position 34, shown in FIG. 5,and a lowest height position 36, as shown in FIG. 7. Specifically, toraise the applicator frame 18 to a maximum height 16 above the groundsurface 20, a flow of pressurized air is supplied the air strut 22 thatis sufficient to cause the air strut 22 to extend to its maximum length34, as illustrated in FIG. 5. To lower the applicator frame 18 to itsminimum height 16 above the ground surface 20, pressurized air isallowed to flow out of the air strut 22, so that the air strut 22 canretract to its minimum length 36, as shown in FIG. 7. By regulating theflow of pressurized air to the air strut 22, the suspension 12 canadjust the length of the air strut 22, and hold the frame 18 of theapplicator at any desired working height 16 by holding extension of theair strut 22 at a corresponding length within the operative strokelength of the air strut 22.

Returning to FIGS. 1 and 2, the frame 18 of the applicator 10 is adaptedfor supporting at least one product container 38 and defines forward andrear ends 40, 42 of the frame 18, a longitudinally extending centralaxis 44 of the frame extending from the rear end 42 to the front end 40of the frame 18, in a direction of travel of the applicator 10, andvertical axis 46 of the frame 18.

FIGS. 3 and 4, illustrate the manner in which the lower suspension arm26, the upper suspension arm 24, and the air strut 22, of the suspensionsystem 12, are operatively interconnected to one another and disposedbetween the rolling axis 30 of the ground engaging wheel 14 and theframe 18, for supporting the applicator 10 above the ground surface 20.

The upper suspension arm 24 defines a frame attachment point 48 of theupper suspension arm 24, that is adapted for attachment to the frame 18.FIGS. 3 and 4 illustrate the suspension system 12 for the right rearwheel 12 of the applicator 10. In the exemplary embodiment of theapplicator 10, the rear wheels 12 are not steerable, so the attachmentpoints 48 of the rear suspension systems 12 are fixedly attached in anon-rotatable manner to the frame 18. Because the front wheels of theexemplary embodiment of the applicator 10 are steerable, the frameattachment points 48 for the front suspension systems 12 are attached tothe frame in a manner that allows the upper suspension arms 22 of thefront wheels to pivot about generally vertically extending steering axes(not shown) with respect to the frame 18, as part of a steeringmechanism (not shown) of the applicator 10.

The lower suspension arm 26 defines the rolling axis 30 of the groundengaging wheel 12 and is adapted for supportive attachment, to the lowersuspension arm 26, of the ground engaging wheel 12, for rotation of theground engaging wheel 12 about the rolling axis 30 of the wheel 12. Inthe exemplary embodiment of the applicator 10, each of the four wheelsof the applicator 12 is independently powered by a hydraulic motor unit50 that is mounted on, and solely supported by the lower arm 26 of thesuspension, for driving the wheel 12 about the rolling axis 30.

As further illustrated in FIGS. 3-5, the upper and lower suspension arms24, 26 also each define respective forward 52, 54 and all 56, 58 ends ofthe suspension arms 24, 26. The forward ends 52, 54 of the upper andlower suspension arms 24, 26 are joined to one another by a knee pin 60,best seen in FIG. 3, to form a pivoting connection, that allows forpivoting movement of the lower arm 26 with respect to the upper arm 24about a suspension pivot axis 61 that extends generally parallel to therolling axis 30 of the wheel 12 and is located forward of the rollingaxis 30 of the wheel 12. The aft ends 56, 58 of the upper and lowersuspension arms 24, 26 are located respectively aft of the frameattachment point 48 and rolling axis 30, and are respectively adaptedfor connection to upper and lower ends 62, 64 of the air strut 22.

As shown schematically in FIG. 4, each of the air struts 22 in thesuspension systems of the exemplary embodiment of the applicator 10 isconfigured for receiving a flow of pressurized air from an air powersource 66, and for extending and retracting in response to the flow ofpressurized air, to thereby respectively lower and raise the rollingaxis 30 of the wheel 12 with respect to the frame attachment point 48,in the manner described above in relation to FIGS. 5-7.

The air struts 22 of the exemplary embodiments are air cylinders, eachhaving an internal movable air piston, contained within a rigidcylinder, and connected to a piston rod of the cylinder. The movablepiston and rigid walls of the cylinder form an internal air chamber 72for receipt of the flow of pressurized air from the air power source 66.As pressurized air enters the internal air chamber, the air strut isurged to extend. And, conversely as pressurized air exits the internalchamber, the air strut retracts. Because the cylinder has rigid walls,it provides a substantially solid support at any extended length, andcan be pressurized to hold a wide range of weights at the desiredextended length. In essence, it will be understood that the air struts22 of the exemplary embodiment of the invention have operatingcharacteristics in which an effective spring rate of the air strut isremotely adjustable to provide a wide variety of desired operatingheights, ride characteristics, and operating modes. This providessignificant advantages in a trailing arm suspension system 12, accordingto the invention, over prior approached that used compression springswith fixed spring rates, and over prior systems that utilized airsprings with flexible side walls which were limited to lower operatingpressures.

As indicated in FIG. 3, the air struts 22 of the exemplary embodiment ofthe applicator 10 also include an integral hydraulic shock absorber 70,disposed in a linear relationship to the internal air chamber and pistonarrangement 72. Other embodiments of the invention may not utilize sucha shock absorber.

As will be understood from the forgoing description, the uppersuspension arms 24 of the suspension systems 12 of the exemplaryembodiment of the applicator 10, are rigid, and configured to notarticulate vertically with respect to the frame 18. Furthermore, theforward end 52 of each of the upper suspension arms 24 is located bothforward of and below the frame attachment point 48 for that uppersuspension arm 24.

As illustrated in FIG. 4, a trailing-link suspension system 12,according to the invention, may further include an electronic controlunit 68 that is operatively connected and configured for controlling theflow of pressurized air to the air strut 22 from the air power source66, to thereby control extension and retraction of the air strut 22. Anelectronic control unit 68, according to the invention, may also beconfigured to receive an input signal 74 that is indicative of a desiredheight 16 of the frame 18 of the applicator 10 above the ground surface16 beneath the applicator, and for controlling the air power source 66in a manner causing the air strut 22 and suspension to support the frame18 at the desired height 16. In the exemplary embodiment of theapplicator 10, the air struts 22 in the suspension systems 12 of allfour wheels 14 are controlled by one or more pressurized air sources 66,and one or more controllers 68, that may be cross linked or combinedinto a common air power source 66 and controller 68 for controlling theheight of the frame 18.

The exemplary embodiment of the applicator 10 is operated using amethod, in accordance with the invention, for controlling the height 16of the frame 18 of the self-propelled agricultural product applicator 10above a ground surface 20, by connecting the frame 18 to the four groundsupporting wheels 14 of the applicator 12, using a trailing linksuspension system 12 according to the invention at each wheel 14, andcontrolling a flow of pressurized air to the air struts 22 of thesuspension systems 12, to thereby control extension of the air struts 22and height 16 of the applicator frame 18 above the ground surface 20.

From the foregoing description, it will be apparent that the inventionprovides significant advantages over previous suspension systems,apparatuses and methods for high ground clearance, self-propelled,agricultural product applicators. The incorporation of the air strutinto the suspension system allows the height of the applicator above theground to be continuously controlled at a desired height, throughregulation of the flow of pressurized air to the strut as product isdispensed.

In contrast to prior systems that utilized compression springs, thestruts can be actively controlled to maintain a constant height,independent of the load that the applicator may be carrying at any givenmoment in time. In addition, the ride height may be selected and heldfor a given load, in a manner that was not possible with priorsuspension systems that utilized compression springs or flexible-sidedair springs.

A suspension system, according to the invention, also allows for heightof the applicator to be selectively adjusted for special situations,such as transporting the applicator on a trailer or truck. Bycontrolling the air struts to retract to their lowest position (see FIG.7) even an unloaded applicator can be made to “squat” in a loweredposition, to thereby reduce the overall height of the applicator andtrailer or truck to facilitate movement of the applicator on publicroadways.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) is to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Itis anticipated that skilled artisans may employ such variations asappropriate, and further anticipated that the invention may be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

I claim:
 1. A trailing-arm suspension system for operatively connectinga ground engaging wheel to a frame of a self-propelled agriculturalproduct applicator, where the frame is adapted for supporting at leastone product container and defines forward and rear ends of the frame, alongitudinally extending central axis of the frame extending from therear to the front of the frame in a direction of travel of theapplicator, and a vertical axis of the frame, the suspension systemcomprising, an upper suspension arm, a lower suspension arm, and an airstrut operatively interconnected to one another and disposed between theground engaging wheel and the frame: the upper suspension arm defining aframe attachment point thereof, adapted for fixed attachment to theframe; the lower suspension arm defining a rolling axis of the groundengaging wheel and adapted for supportive attachment thereto of theground engaging wheel for rotation of the ground engaging wheel aboutthe rolling axis of the wheel; the upper and lower suspension arms alsodefining respective forward and aft ends thereof, with the forward endsbeing adapted for operative pivoting connection to one another about asuspension pivot axis extending generally parallel to the rolling axisof the wheel and disposed forward of the rolling axis of the wheel, andthe aft ends of the upper and lower suspension arms being disposedrespectively aft of the frame attachment point and rolling axis, andwith the aft ends of the upper and lower suspension arms beingrespectively adapted for operative attachment thereto of the air strut;and the air strut having an upper end thereof adapted for operativeattachment to the aft end of the upper suspension arm, and also having alower end thereof adapted for operative attachment to the aft end of thelower suspension arm; with the air strut being configured for receivinga flow of pressurized air from an air power source, and for extendingand retracting in response to the flow of pressurized air, to therebyrespectively lower and raise the rolling axis of the wheel with respectto the frame attachment point.
 2. The suspension system of claim 1,wherein the upper suspension arm is rigid, does not articulatevertically with respect to the frame, and the forward end of the uppersuspension arm is disposed below the frame attachment point.
 3. Thesuspension system of claim 1, wherein the suspension system providessole support for the ground engaging wheel attached thereto.
 4. Thesuspension system of claim 3 further comprising a hydraulic motor driveunit operatively attaching the wheel to the lower suspension arm.
 5. Thesuspension system of claim 1, further including an electronic controlunit operatively connected for controlling the flow of pressurized airto the air strut from the air power source, to thereby control extensionand retraction of the air strut.
 6. The suspension system of claim 5,wherein the electronic control unit is configured to receive an inputsignal indicative of a desired height of the frame of the applicatorabove a ground surface beneath the applicator, and for controlling theair power source in a manner causing the air strut to support the frameat the desired height.
 7. The suspension system of claim 1, wherein theair strut further includes a shock absorber.
 8. A self-propelledagricultural product applicator, having a ground engaging wheeloperatively connected to a frame by a trailing-arm suspension system,with the frame being adapted for supporting at least one productcontainer, the frame defining forward and rear ends of the frame, alongitudinally extending central axis of the frame extending from therear to the front of the frame in a direction of travel of theapplicator, and a vertical axis of the frame, and the suspension systemcomprises: an upper suspension arm, a lower suspension arm, and an airstrut which includes a shock absorber operatively interconnected to oneanother and disposed between the ground engaging wheel and the frame;the upper suspension arm defining a frame attachment point thereof,adapted for fixed attachment to the frame; the lower suspension armdefining a rolling axis of the ground engaging wheel and adapted forsupportive attachment thereto of the ground engaging wheel for rotationof the ground engaging wheel about the rolling axis of the wheel; theupper and lower suspension arms also defining respective forward and aftends thereof, with the forward ends being adapted for operative pivotingconnection to one another about a suspension pivot axis extendinggenerally parallel to the rolling axis of the wheel and disposed forwardof the rolling axis of the wheel, and the aft ends of the upper andlower suspension arms being disposed respectively aft of the frameattachment point and rolling axis, and with the aft ends of the upperand lower suspension arms being respectively adapted for operativeattachment thereto of the air strut; and the air strut having an upperend thereof adapted for operative attachment to the aft end of the uppersuspension arm, and also having a lower end thereof adapted foroperative attachment to the aft end of the lower suspension arm; withthe air strut being configured for receiving a flow of pressurized airfrom an air power source, and for extending and retracting in responseto the flow of pressurized air, to thereby respectively lower and raisethe rolling axis of the wheel with respect to the frame attachmentpoint.
 9. The self-propelled agricultural product applicator of claim 8having a two, or more, ground engaging wheels each operatively attachedto the frame by individual trailing arm suspension systems comprising:an upper suspension arm, a lower suspension arm, an air strut and ahydraulic motor drive unit operatively interconnected to one another anddisposed between the ground engaging wheel and the frame for providingsole support of the ground engaging wheel respectively attached to thatsuspension system; the upper suspension arm defining a frame attachmentpoint thereof, adapted for fixed attachment to the frame, and beingrigid and non-articulable vertically with respect to the frame, with theforward end of the upper suspension arm being disposed below the frameattachment point; the lower suspension arm defining a rolling axis ofthe ground engaging wheel and adapted for supportive attachment theretoof the ground engaging wheel for rotation of the ground engaging wheelabout the rolling axis of the wheel; the upper and lower suspension armsalso defining respective forward and aft ends thereof, with the forwardends being adapted for operative pivoting connection to one anotherabout a suspension pivot axis extending generally parallel to therolling axis of the wheel and disposed forward of the rolling axis ofthe wheel, and the aft ends of the upper and lower suspension arms beingdisposed respectively aft of the frame attachment point and rollingaxis, and with the aft ends of the upper and lower suspension arms beingrespectively adapted for operative attachment thereto of the air strut;the air strut having an upper end thereof adapted for operativeattachment to the aft end of the upper suspension arm, and also having alower end thereof adapted for operative attachment to the aft end of thelower suspension arm; and the air strut being configured for receiving aflow of pressurized air from an air power source, and for extending andretracting in response to the flow of pressurized air, to therebyrespectively lower and raise the rolling axis of the wheel with respectto the frame attachment point.
 10. The self-propelled agriculturalproduct applicator of claim 9, further including an electronic controlunit operatively connected for controlling the flow of pressurized airto the air struts of the suspension systems of the two, or more, groundengaging wheels from the air power source, to thereby control extensionand retraction of the air struts.
 11. The self-propelled agriculturalproduct applicator of claim 10, wherein the electronic control unit isconfigured to receive an input signal indicative of a desired height ofthe frame of the applicator above a ground surface beneath theapplicator, and for controlling the air power source in a manner causingthe air struts of the suspension systems of the two, or more, groundengaging wheels to support the frame of the applicator at the desiredheight.
 12. The self-propelled agricultural product applicator 8,wherein the upper suspension arm is rigid, does not articulatevertically with respect to the frame, and the forward end of the uppersuspension arm is disposed below the frame attachment point.
 13. Theself-propelled agricultural product applicator of claim 8, wherein thesuspension system provides sole support for the ground engaging wheelattached thereto.
 14. The self-propelled agricultural product applicatorof claim 13 further comprising a hydraulic motor drive unit operativelyattaching the wheel to the lower suspension arm.
 15. The self-propelledagricultural product applicator of claim 8, further including anelectronic control unit operatively connected for controlling the flowof pressurized air to the air strut from the air power source, tothereby control extension and retraction of the air strut.
 16. Theself-propelled agricultural product applicator of claim 15, wherein theelectronic control unit is configured to receive an input signalindicative of a desired height of the frame of the applicator above aground surface beneath the applicator, and for controlling the air powersource in a manner causing the air strut to support the frame at thedesired height.
 17. A method for controlling the height of a frame of aself-propelled agricultural product applicator above a ground surface,comprising the steps of: connecting the frame to a ground supportingwheel of the applicator using a trailing link suspension systemincluding an upper suspension arm attached to the frame, a lowersuspension arm providing sole support of a ground engaging wheelattached thereto, and an extensible air strut operatively interconnectedbetween the upper and lower suspension arms; and controlling a flow ofpressurized air to the air strut, to thereby control extension of theair strut and height of the applicator frame above the ground surface;wherein: the upper and lower suspension arms defining respective forwardand aft ends thereof, with the forward ends being adapted for operativepivoting connection to one another about a suspension pivot axisextending generally parallel to and disposed forward of a rolling axisof the ground supporting wheel; the aft ends of the upper and lowersuspension arms being disposed respectively aft of the rolling axis; andthe aft ends of the upper and lower suspension arms being respectivelyadapted for operative attachment to the air strut.
 18. The method ofclaim 17, further comprising connecting two or more ground engagingwheels of the applicator to the frame using individual trailing linksuspension systems, each including an upper suspension arm attached tothe frame, a lower suspension arm providing sole support of a groundengaging wheel attached thereto, and an extensible air strut operativelyinterconnected between the upper and lower arms, and controlling a flowof pressurized air to the air struts of the suspension systems, tothereby control respective extension of the air struts and height of theapplicator frame above the ground surface.
 19. A method for controllingthe height of a frame of a self-propelled agricultural productapplicator above a ground surface, comprising the steps of: connectingthe frame to a ground supporting wheel of the applicator using atrailing link suspension system including an upper suspension armattached to the frame, a lower suspension arm providing sole support ofa ground engaging wheel attached thereto, and an extensible air strutoperatively interconnected between the upper and lower suspension arms;and controlling a flow of pressurized air to the air strut, to therebycontrol extension of the air strut and height of the applicator frameabove the ground surface wherein: the upper suspension arm defines aframe attachment point thereof, adapted for fixed attachment to theframe; the lower suspension arm defines a rolling axis of the groundengaging wheel and adapted for supportive attachment thereto of theground engaging wheel for rotation of the ground engaging wheel aboutthe rolling axis of the wheel; the upper and lower suspension arms alsodefine respective forward and aft ends thereof, with the forward endsbeing adapted for operative pivoting connection to one another about asuspension pivot axis extending generally parallel to the rolling axisof the wheel and disposed forward of the rolling axis of the wheel, andthe aft ends of the upper and lower suspension arms being disposedrespectively aft of the frame attachment point and rolling axis, andwith the aft ends of the upper and lower suspension arms beingrespectively adapted for operative attachment thereto of the air strut;the air strut has an upper end thereof adapted for operative attachmentto the aft end of the upper suspension arm, and also has a lower endthereof adapted for operative attachment to the aft end of the lowersuspension arm; and the air strut is configured for receiving a flow ofpressurized air from an air power source, and for extending andretracting in response to the flow of pressurized air, to therebyrespectively raise and lower the rolling axis of the wheel with respectto the frame attachment point.